Constant frequency variable duty cycle PWM

Hi,

I'm doing a university project (mechanical not electrical engineering, hence my lack of knowledge) which requires an analogue signal (from LabVIEW) to be converted into a PWM signal to drive a servo motor.

The servo requires a frequency of 50Hz with the duty cycle controlled by the LabVIEW output (ranging from 1ms to 2ms). I was intending to use a 555 timer, but I can't find a configuration that lets me obtain such a low duty cycle but keep the frequency constant.

Could anyone point me in the right direction for building such a circuit or at least tell me if I'm approaching this the wrong way? I had looked at using op-amps as an alternative but I've found the same problem.

Thanks a bunch,

Stuart

50 hz with a 1-2msec duty sounds just like PPM used to control model R/C servos. Pehaps you sould search for R/C servo testing circuits to get a idea of how to proceed.

You use one timer to generate 50Hz pulses. This triggers a second timer configured as a one-shot whose pulse length varies according to the control signal (voltage-controlled one-shot or monostable vibrator).

What crutschwo said.

**broken link removed**

Look for "Voltage Controlled Pulse Width Oscillator" there.

Ken